For Q.no.2
Since the test tube is tilted the volume of the gas may change as the height of the mercury changes.
The length of the mercury column will be the same but since the mercury column is tilted its effective height will be 10sin30
Hence the pressure will be P+10sin30 atm.
Accordingly the length of the gas column will vary as the pressure varies

5th one.. it forms an abduct.. initially in NH3 there was a lone pair.. due to which's repulsion the bond pairs had to go farther giving an extra bond angle then expected.. but after the formation of abduct.. the lone pair repulsion would decrease letting the bond pairs to get back to the expected geometry resulting in decrease in bond angle